1. Field of the Invention
This invention relates generally to an idle exhaust system for an outboard motor, and more particularly to an improved idle exhaust system for discharging idle exhaust gases through an exhaust discharge port at a housing unit of an outboard motor.
2. Description of Related Art
An outboard motor typically includes a housing unit that can be mounted on an associated watercraft and an internal combustion engine disposed above the housing unit. A support member affixed to the top of the housing unit normally supports the engine. The housing unit carries a propulsion device such as, for example, a propeller to propel the watercraft. The engine powers the propulsion device with a driveshaft and a propulsion shaft extending through the housing unit.
Typically, the outboard motor employs an exhaust system to discharge exhaust gases from the engine. The exhaust system discharges exhaust gases produced at engine speed above idle to a body of water surrounding the outboard motor. The exhaust gases are discharged through, for example, an exhaust conduit and one or more expansion chambers provided in the housing unit and then through a submerged discharge port that is typically formed at a hub of a propeller.
When the engine speed is above idle, the exhaust pressure exceeds the back pressure caused by the body of water. The exhaust gases thus can exit through the submerged discharge port. At about idle speed, however, the exhaust pressure is less than the back pressure and the exhaust gases do not freely exit through the submerged port. An idle exhaust passage thus is provided to discharge exhaust gases that are produced at the idle speed to the atmosphere through an idle port defined at the housing unit above the waterline.
Typically, the idle exhaust system is branched off from the primary exhaust system. The housing unit defines an idle exhaust discharge port at an upper rear portion of the housing unit. An idle exhaust passage connects the discharge port with a portion of the primary exhaust system which is located most closely to the discharge port. For instance, the idle exhaust passage extends from the exhaust conduit or an exhaust passage defined within the support member. The idle exhaust passage thus is short. Although such a short passage does not occupy much space, exhaust energy at the idle speed is not sufficiently reduced. Accordingly, exhaust noise and temperature can be excessive.
A need therefore exists for an improved idle exhaust system for an outboard motor that can sufficiently reduce exhaust energy at idle speed.
In accordance with one aspect of the present invention, an outboard motor includes a housing unit adapted to be mounted on an associated watercraft, and an internal combustion engine disposed above the housing unit. The engine includes a first exhaust passage to discharge exhaust gases therefrom. A lubricant reservoir is disposed below the engine. The motor also includes a second exhaust passage communicating with the first exhaust passage and extending below the lubricant reservoir. The second exhaust passage extends to a first exhaust discharge port communicating with atmosphere. A third exhaust passage has an inlet communicating with the second exhaust passage at a point below the lubricant reservoir. Additionally, the third exhaust passage extends upwardly to a point at about the same elevation as an upper end of the lubricant reservoir, and extends to a second exhaust discharge port disposed higher than the first exhaust discharge port.
In accordance with another aspect of the present invention, an outboard motor comprises a housing unit adapted to be mounted on an associated watercraft. An internal combustion engine is disposed above the housing unit. The engine defines a first exhaust passage to discharge exhaust gases from the engine. The engine additionally defines a lubricant passage through which lubricant flows. A lubricant reservoir member is disposed below the engine within the housing unit to define a lubricant reservoir therein. The lubricant passage communicates with the lubricant reservoir. The lubricant reservoir member defines a second exhaust passage on an outer surface thereof. The housing unit defines third and fourth exhaust passages. The third exhaust passage connects the first and second exhaust passages. The fourth exhaust passage is arranged downstream of the second exhaust passage. The housing unit defines an exhaust discharge port at an end of the fourth exhaust passage. The exhaust discharge port communicates with atmosphere.
In accordance with a further aspect of the present invention, an outboard motor comprises a housing unit adapted to be mounted on an associated watercraft. An internal combustion engine is disposed above the housing unit. The engine defines a first exhaust passage to discharge exhaust gases from the engine. An exhaust conduit extends generally vertically within the housing unit. The exhaust conduit defines a second exhaust passage communicates with the first exhaust passage. The exhaust gases descends the second exhaust passage. A container is disposed below the engine within the housing unit. The container defines a third exhaust passage communicating with the second exhaust passage. The housing unit defines a fourth exhaust passage communicating with the third exhaust passage and defines an exhaust discharge port disposed at an end of the fourth exhaust passage. The exhaust discharge port communicates with atmosphere.